Adams may be interpreted as providing two arguments, the first being the continuity argument used above. The second is a modal argument relying on the Necessity of Identity and a suitably strong modal logic. Suppose there are two objects that are distinguished by accidental features, as it might be one of the spheres, A has a scratch, while the other B does not. Then it is possible that A has no scratch and hence possible that the spheres be indiscernible. If the Principle holds of necessity the